Arrangement for controlling airflow for example in clean rooms

ABSTRACT

A device for controlling airflow between a clean room ( 1 ) and an adjacent room ( 2 ) is described. Channels ( 10, 6 ) lead from the rooms ( 1, 2 ) to a common junction ( 8 ). A ventilation channel ( 9 ) is leading from the common junction ( 8 ) for feeding or carrying off air. In the channel ( 10 ) from the clean room ( 1 ) is included a resistor element for the airflow, while the channel ( 6 ) from the adjacent room ( 2 ) has low hydraulic impedance.

FIELD OF THE INVENTION

The present invention relates to ventilation installations in buildings,where the building is divided into zones or rooms with differing airpurities. In particular, the invention is applicable in the healthsector, operating theatres, etc., and in the industry for clean rooms orin connection with particularly contaminated rooms. However, theinvention is applicable in a number of other ventilation field where itis desirable to prevent or reduce the incorporation of air of particularcontent, or lack of particular content (pollen or other allergens,odours, dust, etc.), from one area to another, such as isolation wardsand sterile rooms.

STATE OF THE ART

Fundamental for all forms of separation/isolation is separaterooms/cubicles/wards. With pollution entrained in the air, one tries toavoid air spreading from a polluted area to a cleaner one. Anothergeneral method is to dilute with clean air. The clean air can befresh/treated air from outside, or air that has been purified beforebeing sent back into the room.

All rooms, for people or animals, must be provided with fresh air(oxygen) and have spent air (air with waste from users and surroundings)removed. To prevent the required air-circulation from carryingcontaminants from a polluted area into a clean area, cleaning and/ordeactivating measures in the airflow from the most contaminated side areused. Such measures are, inter alia, filters, ultraviolet light andadditives to the air flow, which shall deactivate or remove thecontaminants. Such additives can in themselves cause problems if allowedto spread to the cleaner area. In practice, it is difficult tocompletely seal rooms. To prevent chance from deciding which way the airflows in such escapes, a higher pressure (excess pressure) is created onthe cleanest side and lower pressure (sub-pressure) on the less cleanside. This is made by regulating a difference between the amount of airsupplied and removed. Such systems are described by, among others, CDC(Center of Disease Control and Prevention, Atlanta, Draft Guidelines forEnvironmental Infection Control in Healthcare Facilities, 2001). Aproblem in this situation is that air filters that are often used in theairflow from the polluted side become clogged and the amount of airdecreases. Thereby, the intended difference in pressure and polluted airis reduced or even reversed, whereupon polluted air is forced into thecleaner zone. Countermeasures are more inspection and more frequentservice. Control of small differences in pressure is difficult.Therefore, installations are constructed and set up with an“unnecessary” high degree of difference in pressure, in order to makesufficient simple control possible. Another approach is to make thecontrol automatic and connect it to an automatic realignment of fanpower in the ventilation system (U.S. Pat. No. 5,9512,394, U.S. Pat. No.5,810,657). Tight isolates are more exposed to such pressure reversalthan less tight isolates and sometimes demands of minimum leakage (CDC)are made. Another source of pressure reversal is failure in the part ofthe ventilation system (fan) that contributes to a functional differencein pressure, while the opposite port is intact. The ventilation systemwill in such situations contribute to effectively spread contaminatedair. Therefore, expensive backup systems are built to take over in caseof failure. All in all, the backup systems that shall secure the actualfunctions will contribute with a considerable share of the total costs.The reason for this is that current systems, in their basic function,without further security measures, have a limited functional security.

A person suffering from a critical airborne infection (for instancetuberculosis) is hospitalised in an isolation room with sub-pressure,and patients suffering from immunodeficiencies are placed in isolationrooms with excess pressure. If a immunocompromised patient is infectedwith an airborne infection, a need for both types of isolation will bepresent simultaneously. In practice, this is too expensive, and whenconsidering whether to protect the patient or the surroundings, thepatient loses and is placed in isolation with sub-pressure. Thecalculated minimum leakage then provides extra supply of polluted air,and is in such cases a disadvantage. Corresponding problems are alsopresent in relation to surgery on infectious patients and othersituations.

Access paths present a problem. A doorway is a rather large openingcompared to other openings for air in connection with ventilation.Differences in pressure with closed doors disappears when doors areopened, and small thermal differences on each side of the doorway areenough for air to simultaneously flow in one direction in the uppersection, and flow in the other direction in the lower section.Considering the large area represented by a door, this can amount toconsiderable amounts of air. Therefore, it is recommended that thetraffic is reduced to only what is absolutely necessary (CDC). Isolationof patients causes a conflict with the human need to have contact withothers, and patients also have a need for care and treatment. In orderto reduce dissemination of disease in access openings, extra rooms(sluices, transfer closets) are built in connection with the openings,having a door to the special room and to the surroundings/common area.These doors are favourably arranged such that they cannot be openedsimultaneously. This reduces the communication of contamination by firstreducing the transfer to the amount that is mixed in the sluice from thecontaminated zone and then again to the amount of air in the sluice thatescapes to the common areas. Even minor differences in temperaturebetween the rooms can contribute to this leakage becoming quitesubstantial. In an isolation ward with an airborne-infectious patient(sub-pressure), such spreading of contamination will lead the infectiondirectly to central parts of the hospital. By waiting in the sluice, thecontent of the infection can be diluted, but often there are limitedamounts of air accessible, so it takes a long time to attain practicaldilution. Such a waiting period feels bothersome to the personnel (andis therefore ignored), and it is expensive to have personnel waiting.

In industry, small, clean rooms are supplied with a surplus of cleanair. When moving in and out, industry has similar problems as to thoseof the health service.

In rooms with sub-pressure, a defined surplus of air is often drawn out.This can have fatal consequences in the case of fire and smoke, as smokeand gases from the corridor are drawn directly into the sub-pressureroom.

SUMMARY OF THE INVENTION

A first objective of the invention is to obtain a device that in asimple and reliable manner can achieve high security for a suitabledifference of pressure between rooms having different content in theair. This can be achieved even with a high degree of clogging offilters/channels or other forms of strong reduction in the function ofthe ventilation system. In a sub-pressure isolation room, for example,it would be possible to avoid excess pressure even if the ventilatingfan stops and the supply air fan still functions. Even with a verysimple/small back-up ventilating fan or local recycling arrangement, itwould be possible to maintain a certain degree of sub-pressure.

Another object of the invention is to obtain a device that can arrangethe air streams to shift to the doorways when the doors are opened.Thereby, a strong air flow is achieved in said doorways. Thecontaminated air can, by adjusting the doorway and amount of air, behindered completely or to a greater degree, from entering the cleanzone. In this way, good temperature neutralisation between air in thesluice and the other parts of special rooms is achieved, whichcontributes to reduce the pressure of infectious leakage.

A further object of the invention is to achieve a high number of airshifts in sluice systems connected to pressurised/sub-pressurised rooms.By doing so, a quick dilution of air pollution being sucked into orformed in the sluice can be achieved. This provides a lower degree ofexchange of contamination and/or possibility of a quicker transitionwith the same degree of contamination exchange. The sluice itself getsthe quality of quickly tending to a clean room. Thus, one is notdependent on allowing a certain degree of “uncontrolled” leakage inorder to guard against pressure reversal. Thereby, an even higher degreeof purity is achieved, as the supply can be cleansed to the degree ofpurity wanted.

Still another object of the invention is to provide a device that seesthat a ventilation system to a lesser degree is influenced by incidentalvariation in pressure in corridors or other rooms that are connected toaccess roads. Doors opening and closing should neither influence thesurroundings with regards to ventilation.

Still another object of the invention is to provide a device for simplecontrol of a ventilation system, in order for the system to controlitself within each local zone. A control of the total amount ofadded/removed air can take place in a common area where air balancenormally is less critical than in a special room. Additionally, moresystems bordering the same area are stabilised simultaneously. Theindividual excess pressure/sub-pressure systems are in a lesser degreedependent on the pressure conditions in the corridor/common room.Therefore, there is room to accommnondate the demands set by a centralventilation system and/or make other macroscopic appropriate solutions.

Still another object of the invention is to provide a device included ina ventilation system, so that the ventilation system completely orpartially can react to the present local pressure condition and functionindependently of sensors, actuators and other parts of control loops,which easily fail.

Still another object of the invention is to provide a device in aventilation system that combines sub-pressure and excess pressure sothat pollution from the outside is prevented from entering an isolatedzone, simultaneously with pollution from the inside being prevented fromescaping.

Yet another object of the invention is to provide a device in aventilation system with the ability to restrict smoke influx insub-pressure rooms in the event of fire.

These objects are achieved in a device as stated in the appended patentclaim 1. Further embodiments of the invention appear in the subsequentdependent claims.

BRIEF DESCRIPTION OF THE FIGURES

The invention will now be described with reference to the accompanyingdrawings, where:

FIG. 1 illustrates an embodiment of the invention for supply/removal ofair.

FIG. 2 is a sketch of the invention for removal of air.

FIG. 3 is a sketch of the invention for supplying air.

FIG. 4 is a sketch of the invention with a fire damper.

FIG. 5 is a sketch of the invention employed in a sub-pressure isolationroom with sluice patient room and bath room with implied possibility toincrease the amount of recycled air.

FIG. 6 illustrates two devices according to the invention in the samesystem.

FIG. 7 shows compound devices.

FIG. 8 shows an excess pressure isolation room.

FIG. 9 shows a totally isolated room with both sub-pressure and excesspressure.

FIG. 10 shows a pressurized room based on a simple recycling generator.

DETAILED DESCRIPTION OF THE INVENTION

Initially, the invention will be discussed in terms of the sketch shownin FIG. 1.

The centre of the invention is a device or an arrangement with minimumthree connected channels/flow paths where air can flow alternativeroutes depending on local pressure ratio in connected rooms/cells/zones.In at least one airflow route 6 is an arrangement that functions in sucha manner that airflow in 6 gives a certain drop in pressure. Such anarrangement will hereafter be known as a resistor element. The resistorelement, for example in 6, can be any device giving a difference inpressure by airflow, such as a restriction in area, a frame grate, afilter, a device influenced by flow and/or pressure ratio in or inconnection to 6, a device influenced by conditions connected to door(s)between rooms with channels connected to the invention or a combinationof two or more of said possibilities or equivalent. The design ordimension of the airflow route may also constitute or be included as apart in a resistor element. At least one airflow route 10 has low flowresistance/low hydraulic impedance (hereafter called low flowresistance). These airflow routes are hydraulically-connected at one endin a common room 8. The common junction can be a direct connection ofairflow routes or a larger or smaller chamber/room. To this commonjunction is connected at least one additional airflow route 9 throughwhich a certain amount of airflow is forced. The amount of air in theairflow route 9 can be fixed or dependent on conditions in or betweenassociated rooms, in time and space. The airflow routes 6 and 10 extendfrom the common junction 8 to separate rooms, named 1 and 2. Room 1is—or is a part of, a zone or system with special rooms, and thedesignation 1 can comprise this as a whole or only the room beingconnected to 6. 2 is a part of the surroundings/common area as acorridor or a neighbouring/adjacent room to 1. The access route betweenthe rooms 1 and 2 is closable. In the room 1, except from what mightpass through 6, is set up an appropriate imbalance in the amount ofprovided air and air carried away. The room 1 can be relatively tightand said imbalance in the amount of air flow will primarily pass througha resistor element in the airflow route and there bring about adifferential pressure between the room 1 and the common junction 8. Evenif the room 1 is less tight, a sufficient amount of air will pass viathe resistor element in the airflow route 6, until a favourabledifferential pressure between the room 1 and the common junction 8.Because of the low hydraulic impedance in the airflow route 10, thedifference in pressure over the resistor element in the airflow route 6will practically be equal to the difference in pressure between therooms 1 and 2, independent of the amount of airflow in the airflow route10. If the resistor element is the type where pressure changesrelatively little if the amount of air in the airflow route 6 varies,perhaps within a certain range of quantity, the difference in pressurebetween the rooms 1 and 2 will change little even if the relative degreeof tightness of 1 is not exactly small.

The airflows to or from the common junction 8 are, in total, equal to 0.As the airflow in the airflow route 9 is stronger than the airflow inairflow route 6, with a closed door, one can secure either that suppliedair having the quality in 9, or by collecting all air flowing through 6.Upon free passage (open door(s)) between the rooms 1 and 2, thedifference in pressure between 1 and 2 drops till near zero, because ofthe very low hydraulic impedance represented by an open door.Furthermore, because of the very low hydraulic impedance between theroom 2 and the common junction 8, all or a certain amount of the airflowthat went through airflow route 6 when the door was closed, now mustpass through the doorway and airflow route 10. In the following, theterm resistance channel will be used on airflow route 6, the termreference channel on airflow route 10 and the term ventilation channelon airflow route 9. 1 is called special volume and 2 reference volume.

Net airflow through the doorway contributes to air flowing from clean topolluted zone, so that the amount of air flowing the opposite way isreduced or even becomes equal to zero. In order to strengthen theeffect/provide even better margins; a limited doorway can be used fortraffic which does not demand a completely open doorway. Alternativelyand/or in addition, a system can be arranged to increase the totalamount of airflow so that the mean airflow density/speed through thedoorway becomes higher than it otherwise would have been.

The airflow in the ventilation channel 9 can be from a part of a centralventilation system, a separate ventilation system that collects/deliversair outside the building/construction, air that is collected/deliveredwithin the building/construction (recycled) or a combination of theabove mentioned. Air that is recycled so that it is brought from apolluted area to a cleaner area must be adequately cleansed/inactivated.Said air can also undergo other forms of air treatment, i.e. heating,cooling and/or regulation of humidity, ionization, neutralization,scenting, etc.

In connection with rooms/zones, a plurality of devices for ventilationcan be present, which all work simultaneously and parts of devices canbe shared between several rooms/zones. Variants are to establishconnections 6, 6′, 6″, . . . from junction 8 to the same room or toseveral rooms 1,1′, 1″, . . . with access route to corresponding commonroom 2 or 2,2′, 2″, . . . , with their connections 10, 10′, 2″, . . . ,and where predetermined amounts of air are supplied or carried off in 9or 9,9′, 9″, . . . In a practical embodiment, there might be any numberof said components: 6,1,10,2,9, including one and above.

Examples of means used to achieve a total system, can be developed froman example with a sub-pressure isolation room consisting of a sluiceaccessible from a corridor, a patient room accessible from the sluiceand a bathroom accessible from the patient room. Basically, all ventsare placed in the bathroom and air is provided in an outer deviceaccording to the invention above (the outer) door between the corridorand sluice (6 leads to sluice and 10 to corridor). With closed doors(access roads), the air passes overflow vents or specific resistorelements so that the air pressure gradually falls from room to room inthe isolate. The opening of doors generates a net airflow through thedoorways, said net airflow being equal for all doors except for changesthat might be caused by air leakages. The amount of air in question canbe the amount of fresh air needed to renew the air to be breathed. Oftenit might be desirable to increase the amount of air to get more netairflow through the doorway and/or achieve a quicker dilution of the aircontaminants produced in the isolation ward. Then the amount of freshair passing through the isolation ward can be increased. However, thisoften results in extra expenses for air treatment or it requires heavyinvestments and considerable space for installing channels. Thenpurified air being recycled locally can be used. The recycling functioncan be practised for a larger or smaller part of the isolation ward.Often, it is practical to avoid recycling air from bathrooms/toiletbecause of smell. Air is then often extracted from the patient room,treated and returned to the patient room or to another place furtheraway. By recycling air to ventilation channel 9 in the outer device, anincreased inwards airflow will arise by opening of the two outermostdoors and simultaneous quicker dilution of air contaminants in both thesluice and in patient room(s). If there is too much airflow in thesluice when doors are closed, according to the invention the recycledair can be brought, in an inner device above the door, between thesluice and patient room(s). Compared to this device, the sluicecorresponds to reference volume 2 and the patient room to special volume1. The inner device can have an overflow device in parallel, between 1and 2. By regulating/dimensioning of this overflow device, the amount ofair desired to pass through the sluice while the door is closed can beregulated/dimensioned.

In reference channel 10, in the outer device, a fire damper can beplaced. In case of fire or smoke/gas in the reference volume 2, thisfire damper can be closed. Thus, an excess pressure in the sluice arisesand smoke/gas/heat is hindered from being sucked up into the isolationward, with the consequences that might entail.

By dimensioning the inner device to amounts of air giving full isolationto airborne infections, even with the door between the sluice andpatient room open, the infection leakage from the patient room isindependent from the pressure in the sluice. Further, by reversing theairflow in the outer device and supply the air from the outer device tothe sluice, the sluice is turned into an excess pressure/clean room. Asall leakages from the patient room are sealed, a complete isolation wardthat does not leak airborne infections from the patient room andsimultaneously does not import contaminated air from the outside isachieved. A corresponding arrangement would be suitable for operatingtheatres, etc., for patients suffering from airborne infections.

In principle, clean rooms have the same division between clean andinfected zones. Required air directions and differences in pressure areonly reversed compared to infection isolates.

FIG. 1 illustrates an embodiment of a device comprised by the invention.1 is the room that is to be ventilated (the special volume). 2 is thesurroundings or an adjacent room serving as reference (the referencevolume) for the pressure in the special volume 1. Between the specialvolume 1 and the reference volume 2 is a door 3. 4 is the floor and 5are the ceilings in the rooms. 1 is being ventilated causing animbalance in the amount of air provided or removed. As the specialvolume 1 is relatively closed when the door is shut, the amount of airthat, from the other ventilation in the special volume 1 is imbalanced,is forced through the channel 6 (resistor channel). Because of thechannel's design/dimension or a particular resistor element 7, adifference in pressure between the special volume 1 and the commonjunction 8 arises. The amount: of air passing through the resistancechannel 6 will further pass through the channel 9 (the shaft) and/or thechannel 10 (the reference channel). The amount of air in the shaft 9 canbe adjusted to an appropriate amount. The amount of air in the referencechannel 10 will, dependent on the amounts of air passing through theshaft 9 and the resistance channel 6, be 0 or only a part of the airpassing through the shaft 9. Because of low hydraulic impedance betweenthe common junction 8 and the reference volume 2, these will be onapproximately equal level of pressure even if the airflow in thereference channel 10 is changed. When the door 3 is opened, thehydraulic impedance from the special volume 1 to the common junction 8,via the doorway and the reference channel 10, becomes low and the airwill pass through the doorway instead of through the resistor channel 6.In cases where opening of a door only leads to a reduction of the amountof air in the resistor channel 6 is also a variant of the invention.

FIGS. 2 and 3 are schematic sketches of FIG. 1 with designation of theflow direction for air in the shaft 9. 11 illustrates that air issupplied in the device and 12 illustrates that air is removed (drawnout). FIG. 4 shows the placement of fire damper 12 in the referencechannel. An amount of air larger than that which normally passes throughthe resistor channel 6 is fed into the shaft 9. The surplus passesthrough the reference channel 10 and out in the reference volume 2. Incase of fire and the fire damper 13 closes, all air from the shaft 9will be forced through the resistor channel and into the special volume1 where an excess pressure arises. The excess pressure prevents theinflux of fire-related gases.

FIG. 5 shows the invention used in a sub-pressure isolation room withdoor 3 leading to a corridor 2. Reference numeral 1 is a sluice, 14 is apatient room and 15 an inner room as bathroom/toilet/decontaminationroom etc. Air is carried off from the isolation ward with the ventilator26. Except for special overflow/resistor element 17, 20 or cracks bydoors 18, the isolation ward is relatively airtight. Theoverflow/resistor elements 17, 20 are for simplicity shown in doors 16,19, but can just as well be placed in any other barrier between therooms in question, such as walls. Air that is drawn out by theventilator 26 creates a sub-pressure in the room 15 that draws air fromthe patient room 14 via cracks 18 and/or resistor element/overflowdevice 20 from the sluice 1 and creates sub-pressure there. Finally, airis drawn off into the sluice via the resistor channel 6 in the device 21that takes air from the shaft 9. When air passes a resistor element, adifferential pressure is created so that a gradual dropping pressureextends into the isolation ward. The differential pressure is, amongothers, dependent on the amount of air flowing through the differentresistor elements. If the ventilation 26 is reduced or fails completely,the sub-pressure is reduced and in case of failure, the sub-pressuredisappears. However, excess pressure in the isolation ward does notoccur as air that is blown into the shaft 9 escapes through thereference channel 10. Thermal imbalance can cause some local deviationsin what is described when the differences in pressure are close to zero.When a door is opened, the difference in pressure drops to close to zeroand the air is drawn through the doorway instead. Higher mean air speedis an important element to hinder contamination from passing from thecontaminated side to the clean side. In order to achieve this, it isdesirable to have plenty of air available. It is also desirable withlots of air to achieve a rapid replacement of air or a good reserve tocreate the desired sub-pressure. In FIG. 5, a possible way to increasethe amounts of air in the isolation ward is marked with a broken line.With a recycling generator 23, the amounts of air can be increasedwithout increasing the demand for the amount of air in the ventilator 26and/or the shaft 9. The recycling apparatus can be used simply as areinforcement of the existing ventilation. As there might be problemswith smell in room 15 (e.g. toilet), air is drawn to the generator 23from the patient room 14 with channel 24 and direction 25 as illustratedin FIG. 5. The generator itself contains the necessary means to lead andcleanse the air from the pollutants present. The generator can alsoinclude other forms of air treatment, heating, cooling or other. In thedevice 21, 9 and 22 occur as a combined shaft. Compared to the two outerdoors, the isolation ward functions as before, and the only differenceis that the amount of air is increased. In a constructionally sealedisolation ward, this is illustrated by that the amounts of air in theouter part, which used to be equal to the amount of air in 26, nowequals the sum of the amounts of air in the channels 24 and 26.

FIG. 6 illustrates an alternative for the use of a recycling generatorwhere the air from the generator 23 is fed to a separate device 27. Suchan arrangement can be used when it is not desired to let large amountsof air through the sluice when the door between the sluice and thepatient room is closed. The solutions in FIGS. 5 and 6 can be combinedby letting air from the generator 23 spread to each of the devices 21,27. Another possibility is illustrated in FIG. 7. Air 9 is here fed froma common ventilation system and air 29 from the recycling generator 23to a common shaft in the outer device 28 with reference channel 10 andresistor channel 30. 30 is simultaneously the shaft of a device 31 withreference channel 33 and resistor channel 32. Here, the amount of airwanted through the sluice with closed doors can be determined, dependingon set differences in pressure and leakage 18 between sluice 1 andpatient room 14 and the resistor element 20. When doors are open, thetotal amount of air is available to create barriers to pollution in theopen doors. In case of microbiological pollution, the channel systemscan be equipped with ultraviolet lighting.

FIG. 8 shows an isolation room with excess pressure. Except for the room15, the airflows are equal to the isolation room described in FIG. 5(without the recycling arrangement), only with reversed directions ofairflow and differences in pressure turned around. Again, it is notdesirable to let air from rooms that may carry smell or othernuisances/hazards (15) spread to the other rooms. Air that theprinciples will be applicable just as well for any other room wherethere is a desire to isolate clean air from polluted air. Also, it wouldbe natural to conclude from what is shown, how the principles can beused for more or fewer consecutive rooms.

FIG. 8 shows an excess pressure isolation ward. Except for the room 15,the airflows are similar to the isolation ward described in FIG. 5(without the recycling arrangement) and with reversed directions offlows and differences in pressure. Again, it is not desirable to let airfrom rooms that can allow odour or other nuisances/hazards 15 to spreadto the other rooms. Therefore, air 35 is fed to the patient room 14 anda smaller amount 26 is carried off from room 15. With an additionalrecycling generator, corresponding advantages are achieved, as statedfor the sub-pressure isolation wards illustrated in FIGS. 5, 6 and 7,but for excess pressure isolation wards the direction of air is reversedso that air is fed to the patient room 14.

In FIG. 9, a combined sub-pressure and excess pressure system is shown.Such a system is suitable for immunocompromised patients suffering fromairborne infections, operating theatres for patients suffering fromairborne infections, etc. The patient room 14 and room 15 havesub-pressure compared to the sluice 1. The amounts of air that are drawnoff by ventilators 25 and 26 can be so considerable that even with anopen door, there will not be enough air that flows back from patientroom to sluice. Thus, airborne infection is hindered from coming fromthe patient room. A prerequisite is that the air 26 is adequatelycleansed. A generator of corresponding type as used for recycling can ifnecessary be used. Air 40 is fed to the sluice from the generator 39 andpossibly from the reference channel in device 41, so that air is pressedout through the resistor channel in device 32. This provides the sluice1 with an excess pressure compared to the corridor 2. In FIG. 9 is showna possible connection 46 between the door 3 and the generator 39. Such aconnection can consist of a possible change of amount of air in thegenerator 39 once the door 3 is opened. These and other connections arein principle possible for any generator or central parts of aventilation system.

FIG. 10 illustrates a simple arrangement where a recycling generator 2,3 and a device 8 with reference channel 10, resistor channel 6 and shaft9 provides excess pressure in the room 48 by blowing in air 47. When thedoor/gate 3 is opened, air is drawn out through the doorway/gateway.

The invention is basically illustrated by examples for isolation wards,but any person skilled in the art will understand that the principlescan be utilized just as well for other rooms where separation of cleanair from polluted air is desired. Based on the illustrations, it shouldalso be easy to conclude how the principles could be used for fewer ormore consecutive rooms.

1. A device for controlling airflow, for use in connection withventilation of room/cell/zone, designated the special volume (1), havinga degree of clean air different from surrounding/adjacent rooms,designated the reference volume (2), characterized in a system that isoperated by air pressure alone including a minimum of threechannels/channel systems (6, 9, 10) being hydraulically connected in acommon junction (8), and in that air can be fed or carried off in atleast one of the channels/channel systems, designated the ventilationchannel (9), and that in at least one of the other channels/channelsystems, designated the reference channel(s) (10), is a low hydraulicimpedance from the common junction (8) to the reference volume (2) andthat at least one of the other channels/channel systems (6) extendsbetween the common junction and the special volume (1) and has a designor a device, designated the resistor element (7) which provides asuitable drop in pressure when air flows through and that between thereference volume (2) and the special volume (1) is a closable accesspath (3).
 2. A device according to claim 1, characterized in that in thechannel (9) for feeding/carrying off air, flows an amount of air greaterthan the amount of air flowing in the channel (6) between the commonroom (8) and the special volume (1).
 3. A device according to claim 1,characterized in that except for the amount of air in the associatedsystem, the air is either only fed or carried off in the special volume(1).
 4. A device according to claim 1, characterized in that the specialvolume (1) consists of two or more rooms (14, 15) and thatfeeding/carrying off of air takes place in another room (15) than theroom having a channel connection to the common junction and that betweenthe rooms is/are, in addition to closable access path(s) (16, 19) areoverflow/leakage/resistor elements (17, 18, 20) for air giving asuitable difference in pressure between the rooms (14, 15) at predefinedamounts of air.
 5. A device according to claim 4, characterized in thatfrom the common junction is a corresponding channel connection toseveral independent special volumes (1, 14).
 6. A device according toclaim 4, characterized in that to a special volume (1, 14) with severalaccess paths via separate room(s) in the special volume (1, 14) arechannel connections, from the common room, arranged such that adifference in pressure arises when air flows to more than one of therooms.
 7. A device according to claim 1, characterized in that all orparts of the amount of air flowing through the ventilation channel isair being recycled, with additional cleansing, within the volumesconcerned.
 8. A device according to claim 1, characterized in that thedevice is arranged for feeding of air, and that in the reference channel(10) is inserted a damper that can be closed in case of fire, build-upof smoke, or if other air with particularly dangerous content is presentin the surroundings or in the reference room.
 9. A device according toclaim 1, characterized in that the device is arranged for carrying offair, and that in the channel between the special volume (1) and thecommon junction (8) is inserted a damper that can be closed in case offire, build-up of smoke, or if other air with particularly dangerouscontent is present in the surroundings or in the reference room.
 10. Adevice according to claim 1, characterized in that ultraviolet light isused in the channels/channel systems.
 11. System for controlling airflowin a ventilation system, characterized in that two or more devicesaccording to claim 1 are associated with the same room in a specialvolume (1, 14).
 12. System according to claim 11, characterized in thatthe common junction on a device is connected to the common junction inanother device by means of a reference channel.